The invention concerns a process for the production of a lead accumulator having an electrolyte in the form of a thixotropic gel which as essential constituents includes sulphuric acid and a gel-forming agent.
Such accumulators are independent of position, leak-resistant and maintenance-free and therefore afford advantages over lead accumulators with a liquid electrolyte.
German patent specification No. 3 521 200 describes a process for the production of such lead accumulators, in which, after installation of the electrodes and separators, sulphuric acid which is free from gel-forming agent is firstly poured in in order to completely impregnate the pores of the active materials in the electrodes and the separators and exchange any forming acid which is possibly still present in the pores of the electrodes. Then the excess of that filling electrolyte is completely removed by pouring it out, whereupon the electrolyte space is filled in a second filling step with the electrolyte which is in the form of a thixotropic gel. This process has disadvantages from the point of view of the operating procedure involved as the sulphuric acid has to be completely poured out after the first filling step, which is a tedious operation and which frequently has the result that residues of the filling electrolyte remain in the electrolyte space and only incompletely mix with the thixotropic gel after the latter has been introduced, and therefore give rise to non-homogenous filling of the electrolyte space. In addition, the step of introducing the thixotropic gel which is pre-prepared outside the electrolyte space is a tedious one as it can already revert in the filling operation from the liquefied form to the solid form.
In the process described in German laid-open application (DE-OS) No. 3 644 420 the ripened plates are firstly sulphated in the battery box using gel-free sulphuric acid so that all the sulphuric acid which is required for setting the final acid density of the operating electrolyte is stored as lead sulphate in the active masses of the plates, whereupon the remaining sulphuric acid has to be tipped out in order then to introduce a water/gel-forming agent mixture. Formation of the plates then occurs. That process admittedly eliminates the complicated operation of introducing the thixotropic gel which is produced outside the battery box, but it does not eliminate the step of tipping out surplus sulphuric acid from the sulphating stage. This process also involves the risk of non-homogeneity of the thixotropic gel in the electrolyte space.
The process disclosed in German laid-open application (DE-OS) No. 4 202 497 also involves operating in two steps, wherein in a first step the pores in the active masses in the electrodes and separators are impregnated with sulphuric acid which is free from gel-forming agent and then in a second step the electrolyte space is filled with the electrolyte which is in the form of a thixotropic gel. In the first filling stage the amount of sulphuric acid which is free from gel-forming agent is such that there is no freely movable electrolyte in the cell so that the step of pouring out sulphuric acid is eliminated. It is however difficult to fill all pores without having an excess of sulphuric acid in the first filling stage so that the process is complicated and frequently results in layered and thus non-homogenous filling of the electrolyte space.
Similarly European patent specification No. 0 374 187 concerns a two-stage process in which firstly the ripened plates, after being fitted into the battery box, are wetted and formed with gel-free sulphuric acid, whereupon the surplus acid is tipped out and replaced by a mixture of alkali polysilicate solution with sulphuric acid of appropriate concentration. This process also suffers from the above-indicated disadvantages of two-stage processes.
European laid-open application No. 0 491 150 describes a process in which unformed plates are fitted into the battery box, whereupon the electrolyte space is filled with the dilute sulphuric acid containing gel-forming agents and then the electrode plates are formed. That process is time-consuming and results in non-homogeneity of the gel-like electrolyte.
In U.S. Pat. No. 4,687,718, similarly to German laid-open application (DE-OS) No. 3 644 420, the unformed plates which are fitted into the battery boxes are firstly wetted with sulphuric acid of suitable concentration, whereupon the acid is tipped out and replaced by sulphuric acid containing gel-forming agent. Block box formation is then effected.
All those known processes are carried out in two steps, which involves the disadvantage of dealing with sulphuric acid at a number of points in the operating procedure, possibly with intermediate cleaning steps, and which, due to the required step of tipping out sulphuric acid in the first filling stage, inevitably results in non-homogeneity of the thixotropic gel-like electrolyte in the electrolyte space.